This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application POWER SUPPLYING DEVICE FOR ELECTRON GUN IN CDT filed with the Korean Industrial Property Office on May 4, 2001 and there duly assigned Ser. No. 24453/2001.
1. Technical Field
The present invention relates in general to a power-supplying apparatus for an electron gun in a color display tube (CDT) and, more particularly, to a power-supplying apparatus for an electron gun in a color display tube, which is provided with a fly back transformer (FBT) including an acceleration voltage output terminal and a focus voltage output terminal being connected to an acceleration grid and a focus grid, respectively.
2. Description of the Related Art
A color display tube (CDT) is a picture display apparatus allowing a cathode-ray tube to emit an electron beam according to video signal from a signal source, and allowing a fluorescent substance on a fluorescent panel to emit light by collision with the emitted electron beam, thereby displaying a picture on the panel.
Generally, the color display tube reproduces a predetermined color picture on the fluorescent picture by collision with the electron beam emitted from three electron guns, passing through a shadow mask after acceleration by high voltage (HV+).
With reference to power supplying devices for electron guns, we have detected that a voltage of an acceleration voltage output terminal can fluctuate in an unstable manner depending upon a voltage change of focus voltage output terminals. Accordingly, a screen can become dim, or an iridescent phenomenon may appear on the screen.
Accordingly, the present invention has been made keeping in mind the above-described shortcomings and user""s need, and an object of the present invention is to provide a power supplying apparatus for an electron gun in a color display tube, which can recover voltage of a focus voltage output terminals in fly back transformer dropped by a discharge in the electron gun into normal voltage.
These objects and other objects of the present invention may be accomplished by the provision of a power-supplying apparatus for an electron gun in a color display tube provided with an fly back transformer comprising a focus voltage output terminal and an acceleration voltage output terminal, further comprising a power supplying part supplying a predetermined reference voltage; a focus voltage detection part detecting a focus voltage of the focus voltage output terminal; a focus voltage boost part boosting the focus voltage of the focus voltage output terminal in case that the focus voltage detected by the focus voltage detection part is lower than the reference voltage of the power supplying part.
Here, the focus voltage detection part includes a detection resistance connected in series to the focus voltage output terminal, and can easily detect the focus voltage. The focus voltage boost part comprises a voltage boost circuit provided with a resistance and a capacitor between the power supplying part and the focus voltage detection part, charging therein the reference voltage from the power supplying part, to thereby recover loss of the focus voltage.
Desirably, the power supplying part comprises a vertical and dynamic waveform power-supplying part of the fly back transformer. The focus voltage boost part includes a diode cutting off an inverse electric current from the focus voltage detection part to the power supplying part.
To the acceleration voltage output terminal is provided a by-pass capacitor for maintaining an acceleration voltage, and the voltage of the acceleration voltage output terminal is prevented from fluctuating due to the voltage change of the focus voltage output terminals.
According to another aspect of the present invention, the above objects and other objects may be also achieved by the provision of a method for recover a normal focus voltage of an electron gun in a color display tube, comprising the steps of detecting a focus voltage applied to a focus grid of the electron gun; comparing the focus voltage with a predetermined reference voltage; and boosting the focus voltage applied to the focus grid in case that the focus voltage is lower than the reference voltage.
The reference voltage is voltage of a vertical and dynamic waveform power-supplying terminal applied to the focus grid. The step of boosting the focus voltage comprises the step of supplying voltage charged by a capacitor and a resistance between the focus grid and the vertical and dynamic waveform power-supplying terminal to the focus grid, thereby effectively boosting the focus voltage.
The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example. Other advantages and features will become apparent from the following description and from the claims.